Phosphor coating systems and methods for light emitting structures and packaged light emitting diodes including phosphor coating

ABSTRACT

Methods are disclosed including applying a layer of binder material onto an LED structure. A luminescent solution including an optical material suspended in a solution is atomized using a flow of pressurized gas, and the atomized luminescent solution is sprayed onto the LED structure including the layer of binder material using the flow of pressurized gas.

BACKGROUND

This invention relates to coating of semiconductor devices. Inparticular, this invention relates to methods for spray-coatingsemiconductor light emission structures with layers of phosphor and/orother particles.

Light emitting diodes (LEDs) are semiconductor devices that convertelectric energy to light. Inorganic LEDs typically include an activelayer of semiconductor material and a P-N junction formed at aninterface between two oppositely doped layers. When a bias is appliedacross the P-N junction, holes and/or electrons are injected by the P-Njunction into the active layer. Recombination of holes and electrons inthe active layer generates light that can be emitted from the LED. Thestructure of the device, and the material from which it is constructed,determine the intensity and wavelength of light emitted by the device.Recent advances in LED technology have resulted in highly efficientsolid-state light sources that surpass the efficiency of incandescentand halogen light sources, providing light with equal or greaterbrightness in relation to input power.

Conventional LEDs generate narrow bandwidth, essentially monochromaticlight. However, it is highly desirable to generate wide bandwidth,polychromatic light, such as white light, using a solid state lightsource. One way to produce white light from conventional LEDs is tocombine different wavelengths of light from different LEDs. For example,white light can be produced by combining the light from red, green andblue emitting LEDs, or combining the light from blue and amber LEDs.This approach, however, requires the use of multiple LEDs to produce asingle color of light, which can potentially increase the overall cost,size, complexity and/or heat generated by such a device. In addition,the different colors of light may also be generated from different typesof LEDs fabricated from different material systems. Combining differentLED types to form a white lamp can require costly fabrication techniquesand can require complex control circuitry, since each device may havedifferent electrical requirements and/or may behave differently undervaried operating conditions (e.g. with temperature, current or time).

Light from a blue emitting LED has been converted to white light bysurrounding the LED with a yellow phosphor, polymer or dye, such ascerium-doped yttrium aluminum garnet (Ce:YAG). The phosphor materialabsorbs and “downconverts” some of the blue light generated by the LED.That is, the phosphor material generates light, such as yellow light, inresponse to absorbing the blue light. Thus, some of the blue lightgenerated by the LED appears to be converted to yellow light. Some ofthe blue light from the LED passes through the phosphor without beingchanged, however. The overall LED/phosphor structure emits both blue andyellow light, which combine to provide light that is perceived as whitelight.

LEDs have been combined with phosphor layers by dispensing a volume ofphosphor-containing encapsulant material (e.g., epoxy resin or silicone)over the LED to cover the LED. In these methods, however, it can bedifficult to control the geometry and/or thickness of the phosphorlayer. As a result, light emitted from the LED at different angles canpass through different amounts of conversion material, which can resultin an LED with non-uniform color temperature as a function of viewingangle. Because the geometry and thickness is hard to control, it canalso be difficult to consistently reproduce LEDs with the same orsimilar emission characteristics.

Another conventional method for coating an LED is by stencil printing.In a stencil printing approach, multiple light emitting semiconductordevices are arranged on a substrate with a desired distance betweenadjacent LEDs. The stencil is provided having openings that align withthe LEDs, with the holes being slightly larger than the LEDs and thestencil being thicker than the LEDs. A stencil is positioned on thesubstrate with each of the LEDs located within a respective opening inthe stencil. A composition is then deposited in the stencil openings,covering the LEDs, with a typical composition being a phosphor in asilicone polymer that can be cured by heat or light. After the holes arefilled, the stencil is removed from the substrate and the stencilingcomposition is cured to a solid state.

Like the volumetric dispense method described above, the stencilingmethod may also present difficulties in controlling the geometry and/orlayer thickness of the phosphor containing polymer. The stencilingcomposition may not fully fill the stencil opening, resulting innon-uniform layers. The phosphor-containing composition can also stickto the stencil opening, which may reduce the amount of compositionremaining on the LED. These problems can result in LEDs havingnon-uniform color temperature and LEDs that are difficult toconsistently reproduce with the same or similar emissioncharacteristics.

Another conventional method for coating LEDs with a phosphor utilizeselectrophoretic deposition (EPD). The conversion material particles aresuspended in an electrolyte based solution. A plurality of LEDs areimmersed in the electrolyte solution. One electrode from a power sourceis coupled to the LEDs, and the other electrode is arranged in theelectrolyte solution. The bias from the power source is applied acrossthe electrodes, which causes current to pass through the solution to theLEDs. This creates an electric field that causes the conversion materialto be drawn to the LEDs, covering the LEDs with the conversion material.

After the LEDs are covered by the conversion material, they are removedfrom the electrolyte solution so that the LEDs and their conversionmaterial can be covered by a protective resin. This adds an additionalstep to the process and the conversion material (phosphor particles) canbe disturbed prior to the application of the epoxy. During thedeposition process, the electric field in the electrolyte solution canalso vary such that different concentrations of conversion material canbe deposited across the LEDs. The conversion particles can also settlein the solution, which can also result in different conversion materialconcentrations across the LEDs. The electrolyte solution can be stirredto prevent settling, but this presents the danger of disturbing theparticles already on the LEDs.

Still another coating method for LEDs utilizes droplet deposition usingsystems similar to those in an ink-jet printing apparatus. Droplets of aliquid phosphor-containing material are sprayed from a print head. Thephosphor-containing droplets are ejected from a nozzle on the print headin response to pressure generated in the print head by a thermal bubbleand/or by piezoelectric crystal vibrations. However, in order to controlthe flow of the phosphor-containing composition from the ink-jet printhead, it may be necessary for the print head nozzle to be relativelysmall. In fact, it may be desirable to engineer the size and/or shape ofthe phosphor particles to prevent them from catching in the nozzle andclogging the print head.

SUMMARY

Some embodiments of the invention provide methods including applying alayer of binder material onto an LED structure. A luminescent solutionincluding an optical material suspended in a solution is atomized usinga flow of pressurized gas, and the atomized luminescent solution issprayed onto the LED structure including the layer of binder materialusing the flow of pressurized gas. The term “atomize” is used herein ina general sense to refer to reducing a liquid to minute particles or toa fine spray.

The luminescent solution may be sprayed using an air pressurized spraysystem, and/or the layer of binder material may be applied by sprayingthe binder material with an air pressurized spray system.

The luminescent solution may include wavelength conversion particlessuspended in a volatile solvent, and the methods may further includeevaporating the luminescent solution to provide a layer of wavelengthconversion particles on the LED structure.

The luminescent solution may include wavelength conversion particlessuspended in a nonvolatile solvent, the method may further includecuring the nonvolatile solvent to provide a layer including thewavelength conversion particles on the LED structure.

The LED structure may include an LED chip having a top surface and awirebond pad on the top surface, the method may further include bondinga wire to the wirebond pad before spraying the luminescent solution ontothe LED chip.

The LED structure may include an LED wafer, the method may furtherinclude singulating the LED wafer into a plurality of LED chips afterapplying the layer of binder material and after evaporating theluminescent solution.

Evaporating the luminescent solution may include baking the luminescentsolution and/or exposing the luminescent solution to ultraviolet light.

The methods may further include energizing the LED structure to causethe LED structure to emit light, testing the color of light emitted bythe LED structure, and if the color of light emitted by the LEDstructure is not within a predetermined color threshold, sprayingadditional luminescent solution including a phosphor suspended in asolution onto the LED structure, evaporating the additional luminescentsolution to provide an additional layer of phosphor on the LEDstructure, and applying an additional layer of binder material onto theLED structure.

A layer of the binder material on the LED structure an/or a layer of theluminescent solution on the LED structure may each have a thickness ofless than about 1000 μm.

The LED structure may include an LED chip having a top surface and awirebond pad on the top surface, and the methods may further includemounting the LED within an optical cavity of an LED package beforespraying the luminescent solution onto the LED chip.

The methods may further include curing the binder layer, and dispensingan encapsulant material into the optical cavity over the LED chip,thereby covering the LED chip including the layer of phosphor and thelayer of cured binder material with the encapsulant material.

The LED structure may include an LED wafer, and the methods may furtherinclude forming a plurality of electrical contacts on a surface of theLED wafer, and forming a plurality of sacrificial patterns on respectiveones of the plurality of electrical contacts, applying the layer ofbinder material may include applying the layer of binder material to thesacrificial patterns and onto exposed surfaces of the LED wafer betweenthe sacrificial patterns.

The methods may further include removing the sacrificial patterns andthe portion of the binder material on the sacrificial patterns to exposethe plurality of electrical contacts.

The sacrificial patterns do not completely cover top surfaces of theelectrical contacts, so that the applied binder material is at leastpartially on portions of the top surfaces of the electrical contacts.

Some embodiments of the invention provide light emitting structuresincluding a semiconductor light emitting diode (LED) including a p-njunction active layer, a first layer including binder material andhaving a thickness less than about 1000 μm directly on the LED, and asecond layer including phosphor particles. The second layer has athickness less than about 1000 μm and is directly on the first layer sothat the first layer is between the LED and the second layer.

The first layer may include a binder layer sprayed directly on the chipand the second layer may include a phosphor layer sprayed directly onthe binder layer.

The first layer may be thicker than the second layer. In someembodiments, the first layer has a thickness that is about 100 times athickness of the second layer. In further embodiments, the first layerand the second layer have about a same thickness.

The light emitting structure may include a third layer of bindermaterial directly on the second layer. The light emitting structure mayfurther include a fourth layer including light diffuser particles on thethird layer.

The light emitting structure may further include a third layer includingbinder material directly on the second layer and having a thickness lessthan about 1000 μm, and a fourth layer including phosphor particleshaving a thickness less than about 1000 μm directly on the third layerof binder material.

The semiconductor light emitting diode may include an LED wafer and/oran LED chip.

The phosphor particles may include first phosphor particles configuredto emit light at a first dominant wavelength, and the structure mayfurther include a third layer on the second layer and having a thicknessless than about 1000 μm. The third layer may include second phosphorparticles configured to emit light at a second dominant wavelength. Thefirst dominant wavelength is the same as or different from the seconddominant wavelength.

A light emitting structure according to further embodiments of theinvention includes a semiconductor light emitting diode (LED) includinga p-n junction active layer, a first layer including binder materialhaving a thickness less than about 1000 μm directly on the LED, and asecond layer including phosphor particles and having a thickness lessthan about 1000 μm. The second layer is directly on the first layer sothat the first layer is between the LED and the second layer, and athird layer including diffuser particles is on the second layer.

The phosphor particles may include first phosphor particles configuredto emit light at a first dominant wavelength, and the structure mayfurther include a fourth layer on the second layer and having athickness less than about 1000 μm. The fourth layer includes secondphosphor particles configured to emit light at a second dominantwavelength.

Methods of forming a semiconductor light emitting device according tofurther embodiments of the invention, include applying a layer of bindermaterial onto an LED structure, atomizing a luminescent solutionincluding an optical material suspended in a solution using a flow ofpressurized gas and spraying the atomized luminescent solution onto theLED structure including the layer of binder material using the flow ofpressurized gas to provide a first layer of optical material, curing thelayer of binder material, testing a light emission characteristic of theLED structure, and if the light emission characteristic of the LEDstructure is not acceptable, applying a second layer of optical materialon the LED structure.

The first layer of optical material may include a first phosphorparticle that is configured to emit light having a first wavelength inresponse to light emitted by the LED structure, and the second layer ofoptical material may include a second phosphor particle that isconfigured to emit light having a second wavelength, different from thefirst wavelength, in response to light emitted by the LED structure.

Some embodiments of the invention provide a deposition system includinga liquid supply line, a reservoir coupled to the liquid supply line andconfigured to supply a liquid solvent containing particles of opticalmaterial to the liquid supply line, and a spray nozzle coupled to theliquid supply line and configured to receive the liquid solvent from theliquid supply line. A gas line is coupled to the spray head and isconfigured to provide a pressurized gas to the spray nozzle, and acontroller is configured to control a flow of the liquid solvent intothe spray nozzle.

The deposition system may further include a mass flow controllerconfigured to control a second flow of the liquid solvent from thereservoir into the supply line, and the controller may be furtherconfigured to control the mass flow controller.

The deposition system may further include an optical sensor configuredto detect light output by an LED structure, and the controller may beconfigured to control the flow of the liquid solvent into the spraynozzle in response to the detected light output.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate certain embodiment(s) of theinvention. In the drawings:

FIG. 1 is a schematic diagram illustrating a pressurized depositionsystem for coating a light emitting diode (LED) structure with opticalmaterials, according to some embodiments of the invention.

FIG. 2 illustrates a spray nozzle according to embodiments of theinvention.

FIGS. 3A, 3B, 3C and 3D illustrate the application of optical materialsto a mounted LED chip according to some embodiments.

FIG. 4 illustrate the application of optical materials to an LED chipaccording to some embodiments.

FIG. 5 is a flowchart illustrating operations according to someembodiments of the invention.

FIGS. 6A, 6B and 6C illustrate the application of optical materials toan LED wafer according to some embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including” when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present. Itwill also be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “lateral” or “vertical” may be used herein to describe arelationship of one element, layer or region to another element, layeror region as illustrated in the figures. It will be understood thatthese terms are intended to encompass different orientations of thedevice in addition to the orientation depicted in the figures.

Embodiments of the invention are described herein with reference tocross-section illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of the invention.The thickness of layers and regions in the drawings may be exaggeratedfor clarity. Additionally, variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances, are to be expected. Thus, embodiments of theinvention should not be construed as limited to the particular shapes ofregions illustrated herein but are to include deviations in shapes thatresult, for example, from manufacturing.

FIG. 1 is a schematic diagram illustrating a pressurized depositionsystem 100 for coating a light emitting diode (LED) structure 10 withoptical materials, such as luminescent particles and/or diffuserparticles. According to some embodiments, the optical materials aresprayed onto the LED structure 10 by the system 100. As shown in FIG. 1,a supply line 36 supplies a carrier liquid containing the opticalmaterials to a spray nozzle 50. The carrier liquid is sprayed onto anLED structure 10 via the spray nozzle 50. In particular, pressurized gassupplied to the spray nozzle 50 through a high pressure gas supply line44 atomizes the carrier liquid and directs the atomized liquid includingthe optical materials towards the LED structure 10 where the opticalmaterials are deposited, as described in more detail below. (As notedabove, the term “atomize” is used herein in a general sense to refer toreducing a liquid to minute particles or to a fine spray.) The LEDstructure 10 can include an LED wafer, a mounted LED die and/or anunmounted (i.e. bare) LED die. Accordingly, systems and methodsaccording to embodiments of the invention can be used at various stagesof a manufacturing process.

The liquid in the supply line 36 can include, for example, a bindermaterial, such as liquid silicone and/or liquid epoxy, and/or a volatilesolvent material, such as alcohol, water, acetone, methanol, ethanol,ketone, isopropynol, hydrocarbon solvents, hexane, ethylene glycol,methyl ethyl ketone, and combinations thereof. In general, a volatilesolvent dries or evaporates off shortly after being deposited. Avolatile or nonvolatile solvent material can include particles thereinthat are to be deposited onto the LED structure, such as particles of aluminescent material (e.g. a phosphor) and/or particles of alight-scattering material, such as titanium dioxide. The liquid in thesupply line 36 is provided from one of a plurality of fluid reservoirs30A to 30D, which are attached to the supply line 36 through respectiveinput lines 32A to 32D. The flow of liquid through the input lines 32Ato 32D can be carefully controlled by electronically-controlled massflow controllers 34A to 34D, respectively.

As shown in FIG. 1, the reservoirs 30A to 30D can include a solventreservoir 30A that contains a volatile liquid solvent, such as alcohol,water, etc., and a binder reservoir 30B that contains a liquid bindermaterial, such as liquid silicone and/or liquid epoxy. In someembodiments, the solvent reservoir 30A and the binder reservoir 30B caninclude “pure” liquids, that is, liquids that do not contain anyphosphor, diffuser, or other particles therein. The reservoirs 30A to30D can also include a phosphor reservoir 30C that contains a liquidsolvent in which a concentration of phosphor particles is suspended. Insome embodiments, the phosphor reservoir 30C can include phosphorparticles at a concentration that is greater than a concentration atwhich the phosphor particles will be applied onto the LED structure 10.

The reservoirs 30A to 30D can also include a diffuser reservoir 30D thatcontains a liquid solvent in which a concentration of diffuser particlesis suspended. In some embodiments, the diffuser reservoir 30D caninclude diffuser particles at a concentration that is greater than aconcentration at which the diffuser particles will be applied onto theLED structure 10.

One or more of the reservoirs 30A to 30D can be pressurized, so thatflow from the reservoirs 30A to 30D can be obtained by positive pressureinto the supply line 36. In particular, the solvent reservoir 30A andthe binder reservoir 30B can be pressurized. In some embodiments, thephosphor reservoir 30C and/or the diffuser reservoir 30D may not bepressurized, so that flow from the phosphor reservoir 30C and/or thediffuser reservoir 30D may be induced into the supply line 36 bynegative pressure caused by flow through the supply line 36. Thepressure in the liquid supply line 36 need not be high, since the forcefor spraying the liquid onto the LED structure 10 is provided by ahigh-pressure gas line 44.

The flow of liquid through the supply line 36 can be controlled by anelectronically controllable valve 40. When the valve 40 is open, liquidin the supply line 36 is supplied to the spray nozzle 50.

FIG. 2 illustrates a spray nozzle 50 according to embodiments of theinvention in greater detail. Referring to FIGS. 1 and 2, pressurized gas(e.g., pressurized air) generated by a gas pressurizer 42 is supplied tothe spray nozzle 50 through the pressurized gas supply line 44. Thepressurized gas is directed to through a gas outlet port 52 in the spraynozzle 50 that is adjacent a liquid outlet port 51. The flow of liquidthrough the liquid outlet port 51 can be regulated, for example, bycontrolling the position of a retractable pin 53. When the pin 53 isretracted, the liquid outlet port 51 is opened. The flow of pressurizedgas out of the gas outlet port 52 creates a negative pressure gradientrelative to the liquid outlet port 51, which causes liquid dispensedfrom the liquid outlet port 51 to be atomized. The atomized liquid 54 isthen carried by the gas flow from the gas outlet port 52 to the LEDstructure 10, where the atomized liquid 54 flow deposits on the LEDstructure.

As further illustrated in FIG. 1, operations of the mass flowcontrollers 34A to 34D, the electronically controllable flow valve 40,and the gas pressurizer 42 can be controlled by a controller 20 viaelectronic control lines 22, 24, 26. The controller 20 can be aconventional programmable controller and/or can include an applicationspecific integrated circuit (ASIC) configured to control operation ofthe respective elements of the system 100, or a general microprocessoror controller (e.g. computer).

Referring still to FIG. 1, by controlling the operations of the massflow controllers (MFCs) 34A to 34D and the valve 40, the controller 20can control the composition of liquid that is supplied to the spraynozzle 50 through the supply line 36. In particular, the controller 20can cause the MFCs 30A, 30C and 30D to turn off, while the MFC 30B andthe valve 40 are turned on, to thereby supply the binder liquid to thespray nozzle 50. Likewise, the controller 20 can cause the MFCs 30B, 30Cand 30D to turn off, while the MFC 30A and the valve 40 are turned on,to thereby supply only the solvent liquid to the spray nozzle 50. Withthe solvent material from the solvent reservoir 30A flowing, thecontroller 20 can cause the MFCs 34C and/or 34D to release liquidsbearing phosphor particles (in the case of the phosphor reservoir 30C)and/or diffuser particles (in the case of the diffuser reservoir 30D)into the flow in the supply line 36. Accordingly, the controller 20 canprecisely control the composition of material sprayed onto the LEDstructure 10 by the spray nozzle 50.

It will be appreciated that while FIG. 1 illustrates a single phosphorreservoir 30C and a single diffuser reservoir 30D, more reservoirs canbe provided and attached to the supply line through respective MFCsand/or supply valves that can be electronically controlled by thecontroller 20. For example, separate phosphor reservoirs can be providedfor red phosphors, green phosphors, yellow phosphors, blue phosphors,etc., depending on the product requirements. Furthermore, more than onetype of diffuser particle can be selectively provided using differentdiffuser reservoirs. For example, it may be desirable to apply diffuserparticles having a first composition and/or diameter on one part of anLED structure 10 and diffuser particles having a different compositionand/or diameter on another part of the LED structure 10.

It will be further appreciated that a system 100 as illustrated in FIG.1 may be split into several parts, so that, for example, separate supplylines 36 are provided and/or separate spray nozzles 50 are provided. Forexample, a system could have one supply line 36 and nozzle 50 dedicatedto spray-applying a binder material, and a separate supply line 36 andnozzle 50 dedicated to spray-applying phosphor-bearing liquids and/ordiffuser-bearing liquids. Accordingly, many different combinations ofreservoirs, supply lines and spray nozzles are contemplated according tovarious embodiments.

FIG. 1 further illustrates an optical sensor 35 that is configured tosense light 37 emitted by the LED structure 10. For example, the opticalsensor 35 can detect a color point and/or intensity of light emitted bythe LED structure 10. The detected light information can be provided tothe controller 30 via a communication line 28, and can be used as afeedback signal in the control of the operations of the depositionsystem 100, as described in more detail below.

Referring now to FIGS. 3A to 3D, application of optical materials to anLED structure is illustrated. In the embodiments of FIGS. 3A to 3D, theoptical materials are applied to an LED chip or die 70 mounted on asubstrate 60. However, as explained above, optical materials may beapplied in a similar manner to bare (i.e. unmounted) LED die and/or toLED wafers. An LED wafer includes a wafer substrate on which thinepitaxial layers forming an LED active layer have been formed and/ormounted. Accordingly, an LED wafer can include a growth substrate onwhich the epitaxial layers have been grown and/or a carrier substrate towhich the epitaxial layers have been transferred.

As shown in FIG. 3A, an LED chip 70 is mounted on a substrate 60. TheLED chip 70 can be mounted on the substrate 60 through an intermediarystructure, such as a bonding pad and/or submount (not shown). In someembodiments, The LED chip 70 can be mounted in an optical cavity 64defined by a reflector cup 62 that is placed on the substrate 60. Thereflector cup 62 includes an angled reflective surface 66 facing the LEDchip 70 and configured to reflect light emitted by the LED chip 70 awayfrom the optical cavity 64. The reflector cup 62 further includesupwardly extending sidewalls 62A that define a channel for receiving andholding a lens 94 (FIG. 3D).

It will be appreciated that the reflector cup 62 is optional. Forexample, the LED chip 70 could be mounted on a substrate 60, printedcircuit board or other support member without any reflector around theLED chip 70. Moreover, the reflector cup 62 and the substrate 60 couldbe merged together as a unitary structure. The substrate 60 could alsoinclude a leadframe, and a package body may be formed on the leadframesurrounding the LED chip 70 and defining the optical cavity 64.Accordingly, the LED chip 70 could be mounted in many different stylesof packaging, and the present invention is not limited to the particularpackaging configuration shown in the Figures.

Still referring to FIG. 3A, the LED chip 70 can include a wirebond pad72, and a wirebond connection 74 can be formed from the wirebond pad 72to a corresponding contact pad (not shown) on the substrate 60 orelsewhere. However, it will be appreciated that the LED chip 70 could bea horizontal LED chip having both anode and cathode contacts on the sameside of the chip, and could be mounted in flip-chip fashion on thesubstrate 60, so that no bond wire connections may be made to the LEDchip in some embodiments.

Referring to FIGS. 1, 2 and 3A, the controller 20 of the pressurizeddeposition system 100 can cause a liquid binder material 80 to besupplied to the spray nozzle 50 through the supply line 36. For example,the controller 20 can open the MFC 34B and the valve 40 and close theMFCs 34A, 34C and 34D. Any remaining phosphor-bearing solvents in thesupply line 36 can be purged prior to deposition of the binder material.

The liquid binder material 80 is sprayed onto the LED chip 70, forming athin layer of binder material 80 thereon. The binder material may beformed to have a thickness of less than about 1000 μm, and in someembodiments, may have a thickness less than 1 μm. As noted above, theliquid binder material can include a material such as silicone and/orepoxy.

Referring to FIGS. 1, 2, and 3B, after application of the bindermaterial 80, the supply line 36 can again be purged, and a liquidsolvent can be supplied to the supply line 36 by opening the MFC 34A. Adesired concentration of optical materials, such as phosphor particlesand/or diffuser particles can be provided into the supply line 36 bycontrolling the MFCs 34C, 34D. The liquid solvent may in someembodiments include a volatile liquid solvent, such as alcohol and/orany of the volatile solvents listed above. The liquid solvent includingthe optical materials is sprayed onto the LED chip 70, forming a thincoating 90 (e.g., less than 1000 μm, and in some embodiments, less than1 μm) on the binder material 80.

The volatile solvent liquid may then be evaporated off, leaving theoptical materials (e.g., phosphor particles and/or diffuser particles)stuck to the binder material 80. After evaporation of the solvent, theremaining layer of phosphor particles can have a thickness of about 1 μmto about 1000 μm. Accordingly, in some embodiments, a layer of phosphormaterials can be substantially thinner than the layer of bindermaterial. However, in some cases, a non-volatile solvent, such assilicone and/or epoxy resin, may be used as a carrier liquid for thephosphor/diffuser particles, in which case the non-volatile solvent maybe cured to form a layer 90 of optical material over the LED chip 70.

As shown in FIG. 3C, the layer 90 of optical material may be formed onthe LED chip 70 first, and then the layer 80 of binder material can beformed over the layer 90 of optical material. The layer 90 of opticalmaterial may be formed by spraying the liquid solvent including theoptical materials therein onto the LED chip 70 and thenevaporating/curing the solvent before applying the layer 80 of bindermaterial over the layer 90.

Referring to FIG. 3D, after spray-coating the LED chip 70 with thelayers 80, 90 of binder and phosphor material, an encapsulant material92, such as silicone and/or epoxy, can be dispensed to at leastpartially fill the optical cavity 64, and a lens 94, such as a glass orsilicone lens, can be positioned over the LED chip 70. Curing theencapsulant material 92 secures the lens 94 to the structure, while thevertical wall portions 62A of the reflector cup 62 allow the lens totravel as the encapsulant material 92 expands and contracts withheating/cooling cycles.

In some embodiments, spray-coating of binder material layers and opticalmaterial layers can be alternated. For example, referring to FIG. 4, alayer 80A of binder material may be coated onto an LED chip 70 on asubmount 60. A layer 90A of optical material, such as phosphor particlesand/or diffuser particles, can be formed on the layer 80A in the mannerdescribed above. A second layer 80B of binder material can then beapplied onto the layer 90A of an optical material, and a second layer90B of optical material can be applied onto the second layer 80B ofbinder material. In some embodiments, the second layer 80B of bindermaterial can be omitted from between the first layer 90A and the secondlayer 90B of phosphor material.

The first layer 90A and second layer 90B of optical materials caninclude the same or different optical materials. For example, the firstlayer 90A of optical material can include phosphor particles, while thesecond layer 90A of optical material can include diffuser particles, orvice-versa. In some embodiments, the first layer 90A of optical materialcan include phosphor particles configured to convert incident light to afirst wavelength (e.g. yellow), while the second layer 90A of opticalmaterial can include phosphor particles configured to convert incidentlight to a second wavelength, different from the first wavelength (e.g.red). Accordingly, light output by the packaged LED chip 70 can be amixture of primary light emitted by the LED chip 70 and secondary lightemitted by the first layer 90A of phosphor and the second layer 90B ofphosphor. Such light can have improved color rendering propertiescompared to light generated using only one kind of phosphor.

In some embodiments, the first layer of optical material 90A and thesecond layer of optical material 90B can include the same type ofphosphor. For example, referring to FIGS. 1, 4 and 5, a first binderlayer 80A can be applied to an LED structure, such as an LED chip 70(Block 202) using a spray deposition system 100 according to embodimentsof the invention. A first phosphor layer 90A can then be applied to thebinder layer by spray-coating a phosphor-bearing solvent (Block 204).The solvent can then be evaporated and/or cured, depending on whetherthe solvent is volatile or non-volatile, and the binder material can becured to adhere the phosphor particles to the LED chip 70 (Block 206).At this point, the LED structure could be stored, e.g. at roomtemperature, to be later retrieved for further tuning.

The LED structure can then be energized, for example, by applying avoltage across anode and cathode terminals of the device, and theoptical characteristics (e.g., power output, color point, CCT) of thedevice including the first phosphor layer 80A can be measured. Inparticular, the output power (brightness), color point and/or correlatedcolor temperature (CCT) of the LED structure can be measured (Block208). For example, the light output by the LED structure can be measuredby an optical sensor 35, and the results can be provided to thecontroller 20. Testing the LED structure may be easiest when the LEDstructure includes a mounted LED chip. When the LED structure includesan LED wafer, it may be possible to test representative areas/devices onthe wafer instead of testing every device on the wafer, and tune theentire wafer based on the light output from the test locations.

A test is then performed to determine if the optical characteristics ofthe wafer are acceptable, i.e. to see if the wafer meets establishedbinning requirements (Block 210). If the optical characteristics of thestructure are unacceptable, a decision is made at Block 212 whether todiscard the device (Block 216) or rework the device. However, if theoptical characteristics are satisfactory, the manufacturing processproceeds to the next manufacturing step.

If it is determined that the device can be reworked, the light outputfrom the LED structure can be tuned by determining the amount and typeof additional phosphor needed to correct the color point/CCT of thestructure (Block 214). A second binder layer 80B can be applied (Block202) and/or the first binder layer can be reheated so that it againbecomes tacky, and a second phosphor layer 90B of the same or differenttype from the phosphor used in the first phosphor layer 90A can beapplied using the spray deposition system 100 under the direction of thecontroller 20.

In general, the operations of blocks 202-214 can be repeated as desiredto achieve the desired optical characteristics. However, if too muchphosphor is applied, the light emission characteristics may deterioratedue to reabsorption and/or excessive absorption of light from the LEDstructure, at which point the LED structure may fail the test at Block210.

The solvent liquid carrying the binder material can be evaporated/curedafter each coating layer of optical material is applied. Furthermore theliquid binder material can be fully and/or partially cured after eachcoating layer of binder material is applied and/or after the solventliquid applied thereto is evaporated/cured.

FIGS. 6A to 6C illustrate operations associated with coating an LEDwafer according to some embodiments. Referring to FIG. 6A an LED wafer110 is provided. As discussed above, an LED wafer includes a pluralityof thin epitaxial layers that define a light emitting diode structure.The epitaxial layers are supported by a substrate that can include agrowth substrate and/or a carrier substrate. The epitaxial region of theLED wafer 110 can be divided into a plurality of discrete deviceregions, for example, by mesa and/or implant isolation. In someembodiments, dicing streets (i.e. linear regions where the wafer is tobe diced using a dicing saw) and/or scribe lines may already be formedin the LED wafer 110. A plurality of electrical contacts 112 are formedon the LED wafer 110. In particular, each discrete device in the LEDwafer 110 can include at least one electrical contact 112 on a side ofthe wafer on which phosphor is to be applied.

A sacrificial pattern 114 is formed on the electrical contacts 112. Thesacrificial pattern 114 can include a material such as soluble polymerand/or glass, which can be applied and patterned using conventionalphotolithographic techniques. The sacrificial pattern 114 can be alignedwith the underlying electrical contacts 112. Alternatively, thesacrificial pattern 114 can cover only portions of the electricalcontacts 112, with some portions of the electrical contacts 112 beingexposed. In some embodiments, the sacrificial pattern 114 can be widerthan the electrical contacts 112, so that portions of the surface 110Aof the LED wafer 110 adjacent the electrical contacts are also coveredby the sacrificial patterns. All three possibilities are illustrated inFIG. 6A.

Referring still to FIGS. 6A and 6B, one or more layers 90 of opticalmaterial, such as phosphor particles and/or diffuser particles, areapplied to the surface 110A of the LED wafer 110 using a spray nozzle 50of a pressurized deposition system 100 (FIGS. 1 and 2). One or morelayers of binder material (FIGS. 3A to 3D, 4) may also be coated on theLED wafer 110 over and/or under the phosphor layer 90. The layer 90 iscoated onto the surface 110A of the LED wafer 110, and on thesacrificial pattern 114. In some embodiments, the layer 90 may also becoated onto upper portions of the electrical contacts 112 opposite theLED wafer 110.

After spray-coating the LED wafer 110, the sacrificial pattern 114 canbe removed, for example, by exposure to a liquid solvent specific to thesacrificial pattern material, resulting in an LED wafer 110 as shown inFIG. 6C that includes exposed electrical contacts 112 and one or morelayers 90 of optical material on the surface of the LED wafer 110.

In the drawings and specification, there have been disclosed typicalembodiments of the invention and, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being set forth inthe following claims

1. A method, comprising: applying a layer of binder material onto an LEDstructure; and atomizing a luminescent solution comprising an opticalmaterial suspended in a solution using a flow of pressurized gas andspraying the atomized luminescent solution onto the LED structureincluding the layer of binder material using the flow of pressurizedgas.
 2. The method of claim 1, wherein spraying the luminescent solutioncomprises spraying the luminescent solution with an air pressurizedspray system.
 3. The method of claim 1, wherein applying the layer ofbinder material comprises spraying the binder material with an airpressurized spray system.
 4. The method of claim 1 wherein theluminescent solution comprises wavelength conversion particles suspendedin a volatile solvent, the method further comprising evaporating asolvent from the luminescent solution to provide a layer of wavelengthconversion particles on the LED structure.
 5. The method of claim 1,wherein the luminescent solution comprises wavelength conversionparticles suspended in a nonvolatile solvent, the method furthercomprising curing the nonvolatile solvent to provide a layer includingthe wavelength conversion particles on the LED structure.
 6. The methodof claim 1, wherein the LED structure comprises an LED chip having a topsurface and a wirebond pad on the top surface, the method furthercomprising bonding a wire to the wirebond pad before spraying theluminescent solution onto the LED chip.
 7. The method of claim 4,wherein the LED structure comprises an LED wafer, the method furthercomprising singulating the LED wafer into a plurality of LED chips afterapplying the layer of binder material and after evaporating the solventfrom the luminescent solution.
 8. The method of claim 4, whereinevaporating the solvent from the luminescent solution comprises bakingthe luminescent solution and/or exposing the luminescent solution toultraviolet light.
 9. The method of claim 1, further comprising:energizing the LED structure to cause the LED structure to emit light;testing the optical characteristics of the LED structure; and if theoptical characteristics of the LED structure are not within apredetermined binning threshold, spraying additional luminescentsolution comprising a phosphor suspended in a solution onto the LEDstructure, evaporating the additional luminescent solution to provide anadditional layer of phosphor on the LED structure, and applying anadditional layer of binder material onto the LED structure.
 10. Themethod of claim 1, wherein the LED structure comprises an LED chiphaving a top surface and a wirebond pad on the top surface, the methodfurther comprising mounting the LED within an optical cavity of an LEDpackage before spraying the luminescent solution onto the LED chip. 11.The method of claim 10, further comprising: curing the binder layer; anddispensing an encapsulant material into the optical cavity over the LEDchip, thereby covering the LED chip including the layer of phosphor andthe layer of cured binder material with the encapsulant material. 12.The method of claim 1, wherein the LED structure comprises an LED wafer,the method further comprising: forming a plurality of electricalcontacts on a surface of the LED wafer; and forming a plurality ofsacrificial patterns on respective ones of the plurality of electricalcontacts; wherein applying the layer of binder material comprisesapplying the layer of binder material to the sacrificial patterns andonto exposed surfaces of the LED wafer between the sacrificial patterns.13. The method of claim 12, further comprising removing the sacrificialpatterns and the portion of the binder material on the sacrificialpatterns to expose the plurality of electrical contacts.
 14. The methodof claim 12, wherein the sacrificial patterns do not completely covertop surfaces of the electrical contacts, so that the applied bindermaterial is at least partially on portions of the top surfaces of theelectrical contacts.
 15. A light emitting structure, comprising: asemiconductor light emitting diode (LED) comprising a p-n junctionactive layer; a first layer comprising binder material and having athickness less than about 1000 μm, wherein the first layer is directlyon the LED; and a second layer comprising phosphor particles, the secondlayer having a thickness less than about 1000 μm and being directly onthe first layer so that the first layer is between the LED and thesecond layer.
 16. The light emitting stricture of claim 15, wherein thefirst layer comprises a binder layer sprayed directly on the chip andthe second layer comprises a phosphor layer sprayed directly on thebinder layer.
 17. The light emitting structure of claim 15, wherein thefirst layer is thicker than the second layer.
 18. The light emittingstructure of claim 15, wherein the first layer has a thickness that isabout 100 times a thickness of the second layer.
 19. The light emittingstructure of claim 15, wherein the first layer and the second layer haveabout a same thickness.
 20. The light emitting structure of claim 15,further comprising a third layer of binder material directly on thesecond layer.
 21. The light emitting structure of claim 20, furthercomprising a fourth layer including light diffuser particles on thethird layer.
 22. The light emitting structure of claim 15, furthercomprising: a third layer comprising binder material directly on thesecond layer and having a thickness less than about 1000 μm; and afourth layer comprising phosphor particles having a thickness less thanabout 1000 μm directly on the third layer of binder material.
 23. Thelight emitting structure of claim 15, wherein the semiconductor lightemitting diode comprises an LED wafer.
 24. The light emitting structureof claim 15, wherein the semiconductor light emitting diode comprises anLED chip.
 25. The light emitting structure of claim 15, wherein thephosphor particles comprises first phosphor particles configured to emitlight at a first dominant wavelength, the structure further comprising:a third layer on the second layer and having a thickness less than about1000 μm, the third layer comprising second phosphor particles configuredto emit light at a second dominant wavelength.
 26. The light emittingstructure of claim 25, wherein the first dominant wavelength is the sameas the second dominant wavelength.
 27. The light emitting structure ofclaim 25, wherein the first dominant wavelength is different from thesecond dominant wavelength.
 28. A light emitting structure, comprising:a semiconductor light emitting diode (LED) comprising a p-n junctionactive layer; a first layer comprising binder material having athickness less than about 1000 μm directly on the LED; a second layercomprising phosphor particles and having a thickness less than about1000 μm, the second layer directly on the first layer so that the firstlayer is between the LED and the second layer; and a third layer on thesecond layer, the third layer comprising diffuser particles.
 29. Thelight emitting structure of claim 28, wherein the phosphor particlescomprises first phosphor particles configured to emit light at a firstdominant wavelength, the structure further comprising: a fourth layer onthe second layer and having a thickness less than about 1000 μm, thefourth layer comprising second phosphor particles configured to emitlight at a second dominant wavelength.
 30. A method of forming asemiconductor light emitting device, comprising: applying a layer ofbinder material onto an LED structure; atomizing a luminescent solutioncomprising an optical material suspended in a solution using a flow ofpressurized gas and spraying the atomized luminescent solution onto theLED structure including the layer of binder material using the flow ofpressurized gas to provide a first layer of optical material; curing thelayer of binder material; testing a light emission characteristic of theLED structure; and if the light emission characteristic of the LEDstructure is not acceptable, applying a second layer of optical materialon the LED structure.
 31. The method of claim 30, wherein the firstlayer of optical material comprises a first phosphor particle that isconfigured to emit light having a first wavelength in response to lightemitted by the LED structure, and wherein the second layer of opticalmaterial comprises a second phosphor particle that is configured to emitlight having a second wavelength, different from the first wavelength,in response to light emitted by the LED structure.
 32. A depositionsystem, comprising: a liquid supply line; a reservoir coupled to theliquid supply line and configured to supply a liquid solvent containingparticles of optical material to the liquid supply line; a spray nozzlecoupled to the liquid supply line and configured to receive the liquidsolvent from the liquid supply line; a gas line coupled to the sprayhead and configured to provide a pressurized gas to the spray nozzle;and a controller configured to control a flow of the liquid solvent intothe spray nozzle.
 33. The deposition system of claim 32, furthercomprising: a mass flow controller configured to control a second flowof the liquid solvent from the reservoir into the supply line, whereinthe controller is further configured to control the mass flowcontroller.
 34. The deposition system of claim 32, further comprising:an optical sensor configured to detect light output by an LED structure,wherein the controller is configured to control the flow of the liquidsolvent into the spray nozzle in response to the detected light output.